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## org.bouncycastle.crypto.macs
Class CMac

    java.lang.Object
      org.bouncycastle.crypto.macs.CMac

All Implemented Interfaces:
  Mac

Direct Known Subclasses:
  CMacWithIV

public class CMac
extends java.lang.Object
implements Mac

CMAC - as specified at www.nuee.nagoya-u.ac.jp/labs/tiwata/omac/omac.html

CMAC is analogous to OMAC1 - see also en.wikipedia.org/wiki/CMAC

CMAC is a NIST recomendation - see csrc.nist.gov/CryptoToolkit/modes/800-38_Series_Publications/SP800-38B.pdf

CMAC/OMAC1 is a blockcipher-based message authentication code designed and analyzed by Tetsu Iwata and Kaoru Kurosawa.

CMAC/OMAC1 is a simple variant of the CBC MAC (Cipher Block Chaining Message Authentication Code). OMAC stands for One-Key CBC MAC.

It supports 128- or 64-bits block ciphers, with any key size, and returns a MAC with dimension less or equal to the block size of the underlying cipher.

Constructor Summary
`CMac(BlockCipher cipher)` create a standard MAC based on a CBC block cipher (64 or 128 bit block).
`CMac(BlockCipher cipher, int macSizeInBits)` create a standard MAC based on a block cipher with the size of the MAC been given in bits.

Method Summary
`int` | `doFinal(byte[] out, int outOff)` Compute the final stage of the MAC writing the output to the out parameter.
`java.lang.String` | `getAlgorithmName()` Return the name of the algorithm the MAC implements.
`int` | `getMacSize()` Return the block size for this MAC (in bytes).
`void` | `init(CipherParameters params)` Initialise the MAC.
`void` | `reset()` Reset the mac generator.
`void` | `update(byte in)` add a single byte to the mac for processing.
`void` | `update(byte[] in, int inOff, int len)`

Methods inherited from class java.lang.Object
`clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

Constructor Detail

### CMac

    public CMac(BlockCipher cipher)

  create a standard MAC based on a CBC block cipher (64 or 128 bit block). This will produce an authentication code the length of the block size of the cipher.

Parameters:
  `cipher` - the cipher to be used as the basis of the MAC generation.

### CMac

    public CMac(BlockCipher cipher,
                int macSizeInBits)

  create a standard MAC based on a block cipher with the size of the MAC been given in bits.

  Note: the size of the MAC must be at least 24 bits (FIPS Publication 81), or 16 bits if being used as a data authenticator (FIPS Publication 113), and in general should be less than the size of the block cipher as it reduces the chance of an exhaustive attack (see Handbook of Applied Cryptography).

Parameters:
  `cipher` - the cipher to be used as the basis of the MAC generation.
  `macSizeInBits` - the size of the MAC in bits, must be a multiple of 8 and <= 128.

Method Detail

### getAlgorithmName

    public java.lang.String getAlgorithmName()

  Description copied from interface: `Mac`
  Return the name of the algorithm the MAC implements.

  Specified by:
    `getAlgorithmName` in interface `Mac`
  Returns:
    the name of the algorithm the MAC implements.

### init

    public void init(CipherParameters params)

  Description copied from interface: `Mac`
  Initialise the MAC.

  Specified by:
    `init` in interface `Mac`
  Parameters:
    `params` - the key and other data required by the MAC.

### getMacSize

    public int getMacSize()

  Description copied from interface: `Mac`
  Return the block size for this MAC (in bytes).

  Specified by:
    `getMacSize` in interface `Mac`
  Returns:
    the block size for this MAC in bytes.

### update

    public void update(byte in)

  Description copied from interface: `Mac`
  add a single byte to the mac for processing.

  Specified by:
    `update` in interface `Mac`
  Parameters:
    `in` - the byte to be processed.

### update

    public void update(byte[] in,
                       int inOff,
                       int len)

  Specified by:
    `update` in interface `Mac`
  Parameters:
    `in` - the array containing the input.
    `inOff` - the index in the array the data begins at.
    `len` - the length of the input starting at inOff.

### doFinal

    public int doFinal(byte[] out,
                       int outOff)

  Description copied from interface: `Mac`
  Compute the final stage of the MAC writing the output to the out parameter.

  doFinal leaves the MAC in the same state it was after the last init.

  Specified by:
    `doFinal` in interface `Mac`
  Parameters:
    `out` - the array the MAC is to be output to.
    `outOff` - the offset into the out buffer the output is to start at.

### reset

    public void reset()

  Reset the mac generator.

  Specified by:
    `reset` in interface `Mac`

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